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Balanced control of T cell signaling is critical for adaptive immunity and protection from autoimmunity. By combining genetically engineered mouse models, biochemical analyses and pharmacological interventions, we describe an unexpected dual role of the tumor necrosis factor receptor–associated factor 6 (TRAF6) E3 ligase as both a positive and negative regulator of mucosa-associated lymphoid tissue 1 (MALT1) paracaspase. Although MALT1-TRAF6 recruitment is indispensable for nuclear factor κB signaling in activated T cells, TRAF6 counteracts basal MALT1 protease activity in resting T cells. In mice, loss of TRAF6-mediated homeostatic suppression of MALT1 protease leads to severe autoimmune inflammation, which is completely reverted by genetic or therapeutic inactivation of MALT1 protease function. Thus, TRAF6 functions as a molecular brake for MALT1 protease in resting T cells and a signaling accelerator for MALT1 scaffolding in activated T cells, revealing that TRAF6 controls T cell activation in a switch-like manner. Our findings have important implications for development and treatment of autoimmune diseases.

We report the discovery of a novel series of 1,5-bisphenylpyrazoles as potent MALT1 inhibitors. Structure–activity relationship exploration of a hit compound led to a potent MALT1 inhibitor. Compound 33 showed strong activity against MALT1 (IC50: 0.49 μM), potent cellular activity (NF-κB inhibition and inhibition of IL2 production), and high selectivity against caspase-3, -8, and -9. The results of a kinetics study suggest that compound 33 is a non-competitive inhibitor of MALT1 protein.

SummaryMicrovascular endothelial cells maintain a tight barrier to prevent passage of plasma and circulating immune cells into the extravascular tissue compartment, yet endothelial cells respond rapidly to vasoactive substances, including thrombin, allowing transient paracellular permeability. This response is a cornerstone of acute inflammation, but the mechanisms responsible are still incompletely understood. Here, we demonstrate that thrombin triggers MALT1 to proteolytically cleave cylindromatosis (CYLD). Fragmentation of CYLD results in microtubule disruption and a cascade of events leading to endothelial cell retraction and an acute permeability response. This finding reveals an unexpected role for the MALT1 protease, which previously has been viewed mostly as a driver of pro-inflammatory NF-κB signaling in lymphocytes. Thus, MALT1 not only promotes immune cell activation but also acutely regulates endothelial cell biology, actions that together facilitate tissue inflammation. Pharmacologic inhibition of MALT1 may therefore have synergistic impact by targeting multiple disparate steps in the overall inflammatory response.

Bioassay-guided separation of an extract from a Dictyosporium sp. isolate led to the identification of six new compounds, 1–6, together with five known compounds, 7–11. The structures of the new compounds were primarily established by extensive 1D and 2D NMR experiments. The absolute configurations of compounds 3–6 were determined by comparison of their experimental electronic circular dichroism (ECD) spectra with DFT quantum mechanical calculated ECD spectra. Compounds 3–5 possess novel structural scaffolds, and biochemical studies revealed that oxepinochromenones 1 and 7 inhibited the activity of MALT1 protease.

e14075Background: Mucosa-associated lymphoid tissue lymphoma translocation protein-1 (MALT1) is a key mediator of NF-kB signaling and crucial for proliferation and anti-apoptosis in B-cell lymphoma...